1. Field of the Invention
This invention relates in general to a submersible rotary well pump and in particular to a mechanism for lifting the sucker rod associated therewith.
2. Description of the Related Art
A progressing cavity well pump assembly or rotary well pump assembly includes an electric or hydraulic motor located at the surface of the ground. The motor rotatively drives an elongated rod which is attached to a sucker rod. The sucker rod extends downwardly to a rotary well pump placed down in the well in the area of the fluids to be pumped (downhole pump). Conventional rotary well pumps include a rotor having a helical outer surface shaped in the manner of a corkscrew and a stator having a corkscrew-like helical channel on its inside surface. As the rotor turns within the stator, cavities are formed which progress from the bottom of the pump to the top of the pump, thereby transporting fluids up through the pump and into a string of rods (production tubing or "tubing string") that encase the sucker rod.
During the production of oil, particularly in areas having high concentrations of clay, silt or unconsolidated oil sands, the rotor can become stuck inside the stator or an excessively high torque can be exerted on the motor. In such instances, it becomes necessary to raise and then lower the sucker rod to either free up the attached rotor or reduce the driving torque exerted on the motor. Conventionally, this vertical movement of the rotor and sucker rod has been accomplished by moving a work-over rig to the well, disconnecting a substantial amount of surface equipment, and then lifting and lowering the elongated rod and attached sucker rod using a hoist of the work-over rig. The use of such a work-over rig is inconvenient and expensive because of the cost of moving the rig to the well, the cost associated with the disconnection and reconnection of surface equipment, and the substantial loss of production during the time the surface equipment is being disconnected and reconnected.
U.S. Pat. No. 3,062,290 issued Nov. 6, 1962 to Beckett discloses an apparatus having a sucker rod for driving the plunger of a reciprocating oil well pump connected in a tubing string. The apparatus includes a hydraulic cylinder for reciprocating the sucker rod and two separate hydraulic ram cylinders for periodically producing flow reversals to agitate silt and other materials plugging the formation. The flow reversal means includes the tubing string supported by piston rods which are adapted to move periodically up and down in hydraulic ram cylinders. Movement of the piston rods causes movement of the tubing string within a well casing. When the tubing string is lowered, downwardly acting swabs disposed on the tubing string contact the inner surface of the well casing and cause a flow from the well into the formation, thereby unplugging the formation.
U.S. Pat. No. 4,479,537 issued Oct. 30, 1984 to Reed discloses the use of hydraulic cylinders to lift a tubing string out of the casing of an oil well. The hydraulic lifting apparatus is used in connection with an electric motor driven downhole pump located near the lower end of the tubing string. The apparatus includes a clamp for successively gripping and releasing sections of the tubing string to pull the tubing string out of the well casing in stages. The tubing string sections can be removed for the purpose of replacing an electrical connector on the electric motor that powers the downhole pump.
The Reed apparatus requires a removal or disconnection and reconnection of surface equipment in order to be utilized. Accordingly, production downtime is encountered whenever an electrical connector needs to be replaced. In addition, neither the Beckett or Reed apparatus is adapted to be used with a rotary well pump. Heretofore, there has been no convenient and economical lift mechanism which is capable of dislodging a stuck rotor from a stator and either returning the rotor to its original position in the stator or repositioning the rotor within the stator. In particular, there has been no lift mechanism for conducting a lifting operation without a dismantling of surface equipment or piping and without causing a loss of pressure at the surface, thereby permitting substantially continuous production of oil at the well.